This application claims priority to and the benefit of Korean Application No. 2001-32193, field on Jun. 8, 2001 in the Korean Patent Office, the entire disclosure of which is incorporated herein by reference.
The present invention relates to a cathode ray tube having a panel, on which a phosphor screen is formed, that is made flatter and increased in size, and more particularly, to a color selection apparatus for such a cathode ray tube.
Cathode ray tubes (CRTs) are the most widely used type of display device. The CRT has undergone many improvements over the years, but in recent times, much attention has been given to making the CRT flatter, that is, to making a surface of a panel on which a screen is formed flatter. A flatter panel improves picture quality. Also, there have been efforts to increase CRT screen size (i.e., to increase a size of the panel) in order to satisfy consumer demand for larger display sizes for televisions, computer monitors, etc.
With the flattening and increasing in size of the panel, it is necessary to increase a size of a shadow mask, which is part of a color selection apparatus used to realize colors in the CRT. Because of problems associated with increasing the size of the shadow mask, such as a decrease in strength, many manufacturers apply a new type of color selecting apparatus to their CRTs.
In one such CRT color selecting apparatus, a mask which has a plurality of apertures through which electron beams pass is not curved as in conventional CRTs, but is flat such that a predetermined tension can be applied to the mask. U.S. Pat. No. 3,638,063 discloses a color selecting apparatus having an aperture grill-type mask. The aperture grill mask is made from a plurality of strips that are separated by a predetermined distance and supported by a frame in such a manner as to apply tension in a single direction. Thermal expansion occurring during operation of the CRT is absorbed by a tension applied during mounting of the strips. As a result, the problem of doming common in typical shadow masks is prevented.
However, since the strips forming the aperture grill mask are at a minimal thickness of approximately 0.1 mm, and are connected only at their ends to the frame and with no interconnection between the strips, the strips easily vibrate even with the application of a small external impact. U.S. Pat. Nos. 4,926,089, 4,973,283, and 4,942,332 disclose structures in an attempt to eliminate this problem.
In particular, the above-referenced patents disclose masks that are mounted receiving a predetermined degree of tension on a support assembly, and that include a plurality of strips that are separated by slits and coupled by real ties. Also, false ties are formed between the real ties to minimize the visibility of real tie shadows on the screen. This structure will be described in more detail with reference to FIG. 4.
As shown in the drawing, mask 1 mounted in tension on a support assembly (not shown) includes a plurality of strips 3 that are provided in a direction (shown by arrow xe2x80x98yxe2x80x99) and at a predetermined pitch (i.e., a center-to-center spacing) with real ties 5 arranged between strips 3, extending in a horizontal direction (shown by arrow xe2x80x98xxe2x80x99) and at a predetermined pitch, to form slits 7. Also, a plurality of false ties 9 are formed in each of slits 7, false ties 9 extending in the same direction as real ties 5 but not interconnecting adjacent strips 3.
However, during actual operation of the CRT using the above mask structure, shadows of real ties 5 form black lines on the screen. That is, when electron beams are passed through slits 7 of mask 1, electron beams striking real ties 5 cause shadows of real ties 5 to be formed on the screen of the CRT. Since real ties 5 are formed along lines in the horizontal direction (x), black lines are formed on the screen. This significantly reduces picture quality. The present invention has been made in an effort to solve the above problems.
In accordance with the present invention a color selection apparatus for a cathode ray tube is provided that minimizes black lines formed on a phosphor screen, that limits the ability to perceive the black lines to thereby improve picture quality, and which is resistant to vibration as a result of external impact.
A color selection apparatus is provided including a mask formed having a long axis and a short axis, and a frame supporting the mask in one of a long axis direction and a short axis direction. The mask includes a plurality of strips separated by a predetermined distance. A plurality of first beam apertures are as single long slits between the strips in a center portion of the mask. A plurality of second beam apertures are formed on outer portions of the mask on both sides of the center portion of the mask. The second beam apertures are divided into a plurality of individual units within a single column by real bridges and at least one dummy bridge for each individual second beam aperture unit. The dummy bridges extend inwardly from the strips but do not cross completely through the individual second beam aperture units.
According to a feature of the present invention, a tension T, applied to the strips in the area of the mask where the first beam apertures are formed is greater than a tension T2 applied to the strips in the area of the mask where the second beam apertures are formed.
According to another feature of the present invention, the tensions T, and T2 satisfy the following condition:
T2 less than T1xe2x89xa62T2 
According to yet another feature of the present invention, a number of real bridges formed between the second beam apertures in a single column is increased as a distance from the center portion of the mask is increased.
According to still yet another feature of the present invention, a real bridge height Rhw and a dummy bridge height Dhw (both in a direction of the short axis of the mask) satisfy the following condition:
0.5Rhwxe2x89xa6Dhwxe2x89xa62.0Rhw 
According to still yet another feature of the present invention, the dummy bridges are formed from the strips in a direction of the long axis of the mask.
According to still yet another feature of the present invention, the dummy bridges formed on one side of the second beam apertures correspond to the dummy bridges formed on an opposite side of the second beam apertures.